Michelangelo befriends an unstable mutant alligator, who he later names Leatherhead, possesses a strange piece of Kraang technology, but the other Turtles aren't sure whether Leatherhead is a friend or a foe.

Tired of Raphael's constant criticism, Leonardo lets him try his hand at leadership, while Leonardo meets a female ninja, Karai, who tries to lure him to the dark side.